I. Field of the Invention
The present invention relates to data communication. More particularly, the present invention relates to novel and improved techniques for controlling transmit power of multiple channels in a wireless communication system.
II. Description of the Related Art
In a wireless communication system, a user with a remote terminal (e.g., a cellular phone) communicates with another user through transmissions on the forward and reverse links via one or more base stations. The forward link refers to transmission from the base station to the remote terminal, and the reverse link refers to transmission from the remote terminal to the base station. The forward and reverse links are typically allocated different frequencies.
In a Code Division Multiple Access (CDMA) system, the total transmit power from a base station is typically indicative of the total capacity of the forward link since data may be transmitted to a number of users concurrently over the same frequency band. A portion of the total transmit power is allocated to each active user such that the total aggregate transmit power for all users is less than or equal to the total available transmit power.
To maximize the forward link capacity, the transmit power to each remote terminal may be controlled by a power control loop such that the signal quality, as measured by the energy-per-bit-to-noise-plus-interference ratio, Eb/(No+Io), of the signal received at the remote terminal is maintained at a particular threshold or level. This level is often referred to as the power control setpoint (or simply, the setpoint). A second power control loop may be employed to adjust the setpoint such that a desired level of performance, as measured by the frame error rate (FER), is maintained. The forward link power control mechanism thus attempts to reduce power consumption and interference while maintaining the desired link performance. This results in increased system capacity and reduced delays in serving users.
In some newer generation CDMA systems, to support high-speed data transmission, multiple channels may be concurrently used to transmit larger amount of data. These channels may be used to transmit data at different data rates, and may further utilize different processing (e.g., encoding) schemes. Typically, a particular maximum bit rate (e.g., 800 bps) is allocated to each remote terminal for power control of a number of channels. This allocated bit rate would then be used to transmit the measured signal qualities of the transmissions received on multiple channels to provide power control of the channels. The power control becomes more challenging when the operating parameters (e.g., data rate, required energy per bit, and so on) on these channels are not related by defined relationships.
As can be seen, techniques that can be used to effectively control the transmit power of multiple channels based on a given bit rate are highly desirable.